As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Among such secondary batteries is a lithium secondary battery having high energy density and high discharge voltage, on which much research has been carried out and which is now commercialized and widely used.
Based on the appearance thereof, a lithium secondary battery may be classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. Based on the kind of an electrolyte, a lithium secondary battery may be also classified as a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.
A recent trend in the miniaturization of mobile devices has increased the demand for a prismatic battery or a pouch-shaped battery, which has a small thickness. In particular, much interest is currently focused on such a pouch-shaped battery because it is easy to modify the shape of the pouch-shaped battery, the manufacturing cost of the pouch-shaped battery is low, and the pouch-shaped battery is lightweight.
Generally, a pouch-shaped battery is a battery having an electrode assembly and an electrolyte disposed in a pouch-shaped battery case, formed of a laminate sheet including a resin layer and a metal layer, in a sealed state. The electrode assembly mounted in the battery case is configured in a jelly-roll (wound) type structure, a stacked type structure, or a combination (stacked/folded) type structure. A pouch-shaped battery is manufactured by forming a receiving part, in which an electrode assembly will be mounted, at a laminate sheet and thermally welding the laminate sheet or another sheet separated from the laminate sheet or extending from the laminate sheet in a sealing fashion in a state in which an electrode assembly is mounted in the receiving part.
Meanwhile, a stacked/folded type electrode assembly is manufactured through a notching process, a lamination process, a folding process, a packaging process, and degas process, which are sequentially performed.
In the folding process to wind plate-shaped unit cells in a state in which a separation film is disposed between the unit cells so that the unit cells are sequentially stacked, if the velocity of a winding jig is increased to improve process efficiency, the winding jig, which winds the plate-shaped unit cells, flutters or severely shakes in a direction, i.e. an Y-axis direction, perpendicular to an X-axis direction, which is an advancing direction of a web with the result that electrode active material may be separated from the unit cells or dust may be generated.
In order to solve the above problem, therefore, there is a high necessity for a folding device having a specific structure to manufacture a stacked/folded type electrode assembly.